Method, apparatuses, and systems useful in conducting image guided interventions

ABSTRACT

Methods, apparatuses, and systems relating to image guided interventions on dynamic tissue. One embodiment is a method that includes creating a dataset that includes images, one of the images depicting a non-tissue internal reference marker, being linked to non-tissue internal reference marker positional information, and being at least 2-dimensional. Another embodiment is a method that includes receiving a position of an instrument reference marker coupled to an instrument; transforming the position into image space using a position of a non-tissue internal reference marker implanted in a patient; and superimposing a representation of the instrument on an image in which the non-tissue internal reference marker appears. Computer readable media that include machine readable instructions for carrying out the steps of the disclosed methods. Apparatuses, such as integrated circuits, configured to carry out the steps of the disclosed methods. Systems that include devices configured to carry out steps of the disclosed methods.

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Patent ApplicationSer. No. ______, filed Aug. 11, 2003 by Jerome R. Edwards, entitled“METHODS, APPARATUSES, AND SYSTEMS USEFUL IN CONDUCTING IMAGE GUIDEDINTERVENTIONS,” the entire contents of which are expressly incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to computer readable media,apparatuses, systems, and methods that concern image guided medicalprocedures.

2. Description of Related Art

Image guided surgery (IGS), also known as image guided intervention(IGI), has become an established and proven technology field thatenhances a physician's understanding of the location of his instrumentswithin anatomy during therapy delivery. IGI has grown to include2-dimensional (2-D) and 3-dimensional (3-D) applications. Virtualfluoroscopy as described in U.S. Pat. No. 6,470,207, NavigationalGuidance via Computer Assisted Fluoroscopic Imaging, Simon et al., whichis expressly incorporated by reference, discloses how to register thecoordinate system of anatomy in a live operating theatre to that of a2-D fluoroscopic image and then superimpose the real-time movements ofinstruments on that image as icons. U.S. Pat. No. 6,490,467, SurgicalNavigation Systems Including Reference and Localization Frames, Bucholzet al., which is also expressly incorporated by reference, discloses howto register the coordinate system of anatomy in a live operating theatreto that of a 3-D magnetic resonance imaging (MRI) or computed tomography(CT) image volume and then superimpose the real-time movements ofinstruments on that image volume as icons. The techniques disclosed inthese patents combined with other state of the art technologies haveworked well in procedures involving static anatomy. Static anatomy isanatomy that does not move or has very minimal movement with respect toheart beat and respiration, such as the sinuses, long bones, brain, andindividual vertebral bodies of the spine. The use of image guidance isfast approaching the standard of care in neurosurgical tumor resection,spinal implant placement, ear-nose-and-throat (ENT) surgery, andorthopedics.

However, IGI has not made significant inroads into medical proceduresinvolving dynamic anatomy. Dynamic anatomy is anatomy that movessignificantly with respect to heart beat and respiration, such as theheart, lungs, kidneys, liver, and blood vessels. IGI to date is limitedmostly to use in static anatomy medical procedures primarily due to itsusage of static imaging modalities such as single frame fluoroscopy, andsingle volume MRI and CT.

Imaging modalities do exist to capture dynamic anatomy. Modalities suchas electrocardiogram (ECG)-gated MRI, ECG-gated CT and cinematography(CINE) fluoroscopy (e.g., looped CINE fluoroscopy) are readily availablein hospitals worldwide. These dynamic imaging modalities can captureanatomy over an entire periodic cycle of movement by sampling theanatomy at several instances during its characteristic movement and thencreating a set of image frames or volumes. The use of dynamic imagingmodalities in IGI will allow IGI to transcend the boundaries of staticanatomy and administer efficacy benefits to even more medicalprocedures.

U.S. Pat. No. 6,473,635, A Method of and Device for Determining thePosition of A Medical Instrument, Rasche, which is expresslyincorporated by reference, proposes using the ECG waveform emanatingfrom a live patient in the operating theatre to continuously select froma set of images that were gated to ECG data. However, Rasche's proposalwill not work when the patient exhibits an irregular ECG pattern due tothe medical therapies that are being applied to him. Examples of inducedECG irregularity would occur during pacemaker and implantablecardioverter defibrillator lead placement and radiofrequency ablation ofmyocytes to cure tachycardia.

SUMMARY OF THE INVENTION

One embodiment is a method that includes creating a dataset thatincludes images, at least one of those images depicting a non-tissueinternal reference marker, being linked to non-tissue internal referencemarker positional information, and being at least 2-dimensional.

Another embodiment is a method that includes receiving a position of aninstrument reference marker coupled to an instrument; transforming theposition into image space using a position of a non-tissue internalreference marker implanted in a patient; and superimposing arepresentation of the instrument on an image in which the non-tissueinternal reference marker appears.

Other embodiments of the present methods are disclosed below.

Other embodiments include computer readable media that include machinereadable instructions for carrying out the steps of any of the presentmethods. Still other embodiments include apparatuses, such as integratedcircuits, configured to carry out the steps of any of the presentmethods. Other embodiments include systems that include devicesconfigured to carry out steps of the present methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings demonstrate aspects of some of the presentmethods, apparatuses, and systems. They illustrate by way of example andnot limitation. Like reference numbers refer to similar elements.

FIG. 1 shows the layout of a system that may be used to carry out imageguided interventions using certain of the present methods that involvegated datasets.

FIG. 2 is a representation of one of the present gated datasets storedin memory.

FIG. 3 illustrates one example of samples of a periodic humancharacteristic signal (specifically, an ECG waveform) associated, orgated, with images of dynamic anatomy.

FIG. 4 is a flowchart showing an embodiment of a state through which thepresent software may run to perform certain embodiments of the presentmethods.

FIG. 5 is a flowchart showing another embodiment of a state throughwhich the present software may run to perform certain embodiments of thepresent methods.

FIG. 6 shows the layout of a system that may be used to carry out imageguided interventions using certain of the present methods that do notinvolve gated datasets.

FIG. 7 illustrates one example of the link between reference markerpositional information and images of dynamic anatomy.

FIG. 8 is a flowchart showing another embodiment of a state throughwhich the present software may run to perform certain embodiments of thepresent methods.

FIG. 9 is a representation of one of the present datasets stored inmemory.

FIG. 10 is a flowchart showing another embodiment of a state throughwhich the present software may run to perform certain embodiments of thepresent methods.

FIG. 11 illustrates an embodiment of one of the present non-tissueinternal reference markers.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The terms “comprise” (and any form of comprise, such as “comprises” and“comprising”), “have” (and any form of have, such as “has” and“having”), “contain” (and any form of contain, such as “contains” and“containing”), and “include” (and any form of include, such as“includes” and “including”) are open-ended linking verbs. Thus, amethod, an apparatus, or a system that “comprises,” “has,” “contains,”or “includes” one or more items possesses at least those one or moreitems, but is not limited to possessing only those one or more items.For example, a method that comprises receiving a position of aninstrument reference marker coupled to an instrument; transforming theposition into image space using a position of a non-tissue internalreference marker implanted in a patient; and superimposing arepresentation of the instrument on an image in which the non-tissueinternal reference marker appears possesses at least the receiving,transforming, and superimposing steps, but is not limited to possessingonly those steps. Accordingly, the method also covers instances wherethe transforming includes transforming the position into image spaceusing a transformation that is based, in part, on the position of thenon-tissue internal reference marker implanted in the patient, andcalculating the transformation using image space coordinates of theinternal reference marker in the image. The term “use” should beinterpreted the same way. Thus, a calculation that uses certain itemsuses at least those items, but also covers the use of additional items.

Individuals elements or steps of the present methods, apparatuses, andsystems are to be treated in the same manner. Thus, a step that callsfor creating a dataset that includes images, one of the images (a)depicting a non-tissue internal reference marker, (b) being linked tonon-tissue internal reference marker positional information, and (c)being at least 2-dimensional covers the creation of at least such adataset, but also covers the creation of a dataset that includes images,where each image (a) depicts the non tissue internal reference marker,and (b) is linked to non-tissue internal reference marker positionalinformation.

The terms “a” and “an” are defined as one or more than one. The term“another” is defined as at least a second or more. The term “coupled”encompasses both direct and indirect connections, and is not limited tomechanical connections.

Those of skill in the art will appreciate that in the detaileddescription below, certain well known components and assembly techniqueshave been omitted so that the present methods, apparatuses, and systemsare not obscured in unnecessary detail.

Broadly, embodiments of the present methods, apparatuses, and systemsenable the use of dynamic imaging modalities in 2-D and 3-D IGI.Specifically, the various embodiments of the present embodiments of thepresent methods, apparatuses, and systems are useful for allowing aparticular image from a set of images depicting dynamic anatomy to beselected, such that the selected image is the most accuraterepresentation of the instantaneous position and orientation of the liveanatomy in the operating theatre. The locations of the present referencemarkers (in the form of vectors, for example) may be synchronized toeach image in the set of images, and the positional information of themarkers allows a transformation to be calculated between the real worldcoordinate space and the image space for the purpose of superimposingthe live position of one or more instruments onto the selected image.Dynamic anatomy is anatomy that moves significantly with respect toheart beat and/or respiration, such as the heart, lungs, kidneys, liver,and blood vessels.

More specifically, embodiments of the present methods, apparatuses, andsystems are useful for the placing and tracking one or more non-tissueinternal reference markers within a gross anatomic region of interestthat moves periodically with heart beat and respiration, synchronizingthe location or locations of those marker locations with images thatbest describe the specific anatomy of interest in a particularorientation, selecting the image that best describes the anatomy ofinterest at any given moment in the operating or procedure room, andsuperimposing iconic representation of one or more instruments on themost accurate image selected after making the appropriate transformationfrom the tracking space of the instrument to image space. A “non-tissueinternal reference marker” is a reference marker, which is sometimesreferred to in the art as a “fiducial,” that is positioned inside of apatient (e.g., any living being, human or otherwise) and that is notmade from the patient's tissue or other living matter. Embodiments ofthe present methods, apparatuses, and systems may be used in thedelivery of various medical therapies including, but not limited to,pacemaker lead placement, coronary stent placement, cardiac radiofrequency ablation, lung biopsy, renal stent placement, transjugularintrahepatic porto-systemic shunting, and percutaneous radio frequencyablation of renal masses.

IGI has not made significant inroads into medical procedures involvingdynamic anatomy. IGI is suited to, and has been used primarily in,static anatomy medical procedures due to its usage of static imagingmodalities such as single frame fluoroscopy, and single volume MRI andCT. While Rasche (i.e., U.S. Pat. No. 6,473,635) discloses certain IGIwith dynamic anatomy, his proposed method depends on the patient's ECGdata during the operation. That is, Rasche's method involves collectingECG data as the operation is taking place and, based on a given phase ofthat ECG data, displaying an image for viewing by the physician. Such anapproach will not work if the patient exhibits an irregular ECG patterndue to the medical therapies that are being applied to him. Examples ofinduced ECG irregularity would occur during pacemaker and implantablecardioverter defibrillator lead placement and radiofrequency ablation ofmyocytes to cure tachycardia. The present methods, apparatuses, andsystems do not rely on ECG data that is taken as an operation takesplace in order to select the appropriate pre-operative image to displayfor the physician.

Further, Rasche requires the use of an external reference probe incalculating “a simple co-ordinate transformation” between actual spatialand image coordinate systems. An external reference marker will neverproduce the transformation accuracy of an internal reference markerpositioned close to the anatomy of interest—as used by the presentmethods, apparatuses, and systems—due to a moment arm escalation oferror.

1. Use of a Gated Image Dataset

FIG. 1 shows one embodiment of a system (system 100) that includescomponents that can be used to perform image guided interventions usinga gated imaging modality, such as ECG-gated MRI, or ECG-gated CT. Thefigure depicts a patient 10 positioned on an operating table 12 with aphysician 14 performing a medical procedure on him.

Specifically, FIG. 1 depicts physician 14 steering a medical instrument16 through the patient's internal anatomy in order to deliver therapy.In this particular instance, instrument 16 is depicted as a catheterentering the right atrium by way of the inferior vena cava preceded by afemoral artery access point; however, the present systems are notlimited to catheter use indications. The position of virtually anyinstrument may be tracked as discussed below and a representation of itsuperimposed on the proper image, consistent with the present methods,apparatuses, and systems. An “instrument” is any device controlled byphysician 10 for the purpose of delivering therapy, and includesneedles, guidewires, stents, filters, occluders, retrieval devices, andleads. Instrument 16 is fitted with one or more instrument referencemarkers 18. A tracker 20 (which is sometimes referred to in the art as a“tracking system”) is configured to track the type of reference markeror markers coupled to instrument 16. Tracker 20 can be any type oftracking system, including but not limited to an electromagnetictracking system. An example of a suitable electromagnetic trackingsystem is the AURORA electromagnetic tracking system, commerciallyavailable from Northern Digital Inc. in Waterloo, Ontario Canada. Iftracker 20 is an electromagnetic tracking system, element 20 wouldrepresent an electromagnetic field generator that emits a series ofelectromagnetic fields designed to engulf patient 10, and referencemarker or markers 18 coupled to medical instrument 16 could be coilsthat would receive an induced voltage that could be monitored andtranslated into a coordinate position of the marker(s).

An external reference marker 22 can be placed in a location close to theregion of the patient where the procedure is to be performed, yet in astable location that will not move (or that will move a negligibleamount) with the patient's heart beat and respiration. If patient 10 issecurely fixed to table 12 for the procedure, external reference marker22 (which may be described as “static”) can be affixed to table 12. Ifpatient 10 is not completely secured to table 12, external referencemarker 22 can be placed on region of the back of patient 10 exhibitingthe least amount of movement. Tracker 20 can be configured to trackexternal reference marker 22.

One or more non-tissue internal reference markers 24 can be placed inthe gross region where the image guided navigation will be carried out.Non-tissue internal reference marker(s) 24 should be placed in ananatomic location that exhibits movement that is correlated with themovement of the anatomy intended for image guided navigation. Thislocation will be internal to the patient, in the gross location of theanatomy of interest.

Medical instrument 16, instrument reference marker(s) 18, externalreference marker 22, and non-tissue internal reference marker(s) 24 canbe coupled to converter 26 of system 100. Converter 26, one example ofwhich may be referred to in the art as a break-out box, can beconfigured to convert analog measurements received from the referencemarkers and tracker 20 into digital data understandable by imageguidance computing platform 30, and relay that data to image guidancecomputing platform 30 to which converter 26 can be coupled. Imageguidance computing platform 30 can take the form of a computer, and mayinclude a monitor on which a representation of one or more instrumentsused during the IGI can be displayed over an image of the anatomy ofinterest.

System 100 also includes a periodic human characteristic signal monitor,such as ECG monitor 32, which can be configured to receive a periodichuman characteristic signal. For example, ECG monitor 32 can beconfigured to receive an ECG signal in the form of the ECG datatransmitted to it by ECG leads 34 coupled to patient 10. The periodichuman characteristic signal monitor (e.g., ECG monitor 32) can also beconfigured to relay a periodic human characteristic signal (e.g., ECGdata) to image guidance computing platform 30, to which it can becoupled.

Prior to the start of the image guided intervention, non-tissue internalreference marker(s) 24—but not necessarily static external referencemarker 22—should be placed in the gross region of interest for theprocedure. After placement of non-tissue internal reference marker(s)24, patient 10 is to be scanned with an imaging device, such as gatedscanner 40, and the resulting gated image dataset transferred to imageguidance computing platform 30, to which the imaging device is coupledand which can reside in the operating or procedure theatre. Examples ofsuitable imaging devices, and more specifically suitable gated scanners,include ECG-gated MRI scanners and ECG-gated CT scanners. A hospitalnetwork 50 may be used to couple gated scanner 40 to image guidancecomputing platform 30.

The imaging device (e.g., gated scanner 40) can be configured to createa gated dataset that includes pre-operative images, one or more of which(up to all) are taken using the imaging device and are linked to asample of a periodic human characteristic signal (e.g., a sample, or aphase, of an ECG signal). Once patient 10 is scanned using the imagingdevice and the gated dataset is transferred to and received by imageguidance computing platform 30, patient 10 can be secured to operatingtable 12 and the equipment making up system 100 (e.g., tracker 20,converter 26, image guidance computing platform 30, ECG monitor 32, andgated scanner 40) set up as shown in FIG. 1. Information can then flowamong the system 100 components.

At this point, a gated dataset created by gated scanner 40 resides onimage guidance computing platform 30. FIG. 2 shows gated dataset 42residing in memory 44, which can reside in image guidance computingplatform 30. Gated dataset 42 is organized as a set of images (I1, I2,I3, I4 . . . In) that are correlated with periodic human characteristicsignal samples (S1, S2, S3 . . . Sn). In the embodiment shown, theperiodic human characteristic signal is taken to be an ECG signal, orwaveform. FIG. 3 highlights the relationship between the samples (S1 . .. Sn) and the images (I1 . . . In) that were captured by gated scanner40. Designations P, Q, R, S, and T are designations well known in theart; they designate depolarizations and re-polarizations of the heart.Gated scanner 40 essentially creates an image of the anatomy of interestat a particular instant in time during the anatomy's periodic movement.Image I1 corresponds to the image that was captured at the S1 moment ofpatient 10's ECG cycle. Similarly, I2 is correlated with S2, and In withSn.

After the gated scanning has occurred and the system 100 components arecoupled to each other as shown in FIG. 1, software running on imageguidance computing platform 30 can begin its operation sequence. Thesoftware first enters a Calibration State as depicted in FIG. 4. Thegoal of the software during the Calibration State is to construct adataset (which, in at least one embodiment, may be described as alook-up table) with dataset vectors linked to the pre-operative imagescollected by the gating scanner 40. In later states of operation, thelook-up table will allow the software to choose the image that bestdescribes the actual instantaneous orientation of the live anatomy. Eachdataset vector is a magnitude and direction constructed by examining thelocation of static external reference marker 22 and non-tissue internalreference marker(s) 24. In this regard, static external reference marker22 can act as an origin for a dataset vector that begins at origin andends at the internal reference marker(s) 24 location. (Multiple vectorsmay be used if there are multiple non-tissue internal referencemarkers.)

FIG. 4 shows the flow of the Calibration State 60. At step 62, thesoftware can load gated dataset 42 into memory 44 (as depicted in FIG.4). Next, the software can loop through each gated signal sample (S1, S2. . . Sn) while sampling the live periodic human characteristic signalcoming from patient 10 by way of the periodic human characteristicsignal monitor (e.g., ECG monitor 32). In the example shown in thefigures, that signal is, like the first periodic human characteristicsignal used in constructing the gated dataset, an ECG signal orwaveform. Thus, element 64 represents each gated signal sample for whichstep 66—sampling of the live ECG waveform—occurs. At step 68, thesoftware compares the sample from patient 10's live ECG waveform andcompares it to the gated signal sample in question (Si). When thesoftware gets a match (e.g., when the sample from the live ECG waveformmatches gated signal sample Si), it can, at step 70, poll tracker 20 toobtain the positions of static external reference marker 22 andnon-tissue internal reference marker(s) 24 in order to, at step 72,construct, or calculate, a dataset vector (Vi). A match can beascertained using signal processing techniques that, in the case of theECG waveform, examine historical waveform amplitudes. Once the datasetvector is constructed, at step 74, the dataset vector can be stored inthe look-up table with a pointer to the image (Ii) that correspondedwith the gated signal sample (Si) of gated dataset 42. That is, thedataset vector can be linked to, or associated with, that particularimage (Ii). After the software has looped through all the gated signalsamples (S1 . . . Sn) of gated dataset 42, constructed a dataset vector(V1 . . . Vn) for each sample, and linked that dataset vector with theappropriate image (I1 . . . In), the software is ready to move on. Atthis time, the periodic human characteristic signal monitor (e.g., ECGmonitor 32) may be turned off or otherwise removed from system 100—it isno longer needed. In at least one embodiment, the dataset vectorsdescribed above may comprise nothing more than the tracking spacecoordinates of the external reference marker 22 and non-tissue internalreference marker(s) 24; as a result, step 72 is not needed, and thelinking of the dataset vectors to the various images of gated dataset 42will comprise linking the tracking space coordinates of the relevantreference markers to those images.

The final step of Calibration State 60 is a transformation calculationstep. The software will file through each dataset vector in the look-uptable, as noted by element 75, and examine each mapped image. At step76, the image space coordinates of non-tissue internal referencemarker(s) 24 in each image (Ii) will be determined. For example, eachimage (Ii) can undergo a thresh-holding segmentation that will allow thesoftware to find the image space coordinates of non-tissue internalreference marker(s) 24 in that image. Once the image space coordinates(e.g., voxel, volumetric pixel, coordinates) of non-tissue internalreference marker(s) 24 are known, the positions (e.g., the trackingspace positions) of the external reference marker 22 and the non-tissueinternal reference marker(s) 24 received at step 70 can be used tocalculate a transformation (using a least squares method) between thetracking space and the image space. Step 78 is the calculation of such atransformation (Ti), and step 80 is the linking of the transformation(Ti) to the image (Ii) in question. As a result of that linking, thelook-up table will comprise a dataset that includes pre-operativeimages, at least one the images (and, moreover, each image) depictingnon-tissue internal reference marker(s) 24, being linked to a datasetvector and a transformation, and being at least 2-dimensional.

After completion of Calibration State 60, the software moves the systeminto Navigate State 90 as depicted in FIG. 5. In this state, thesoftware can enter an infinite loop of events, as designated by element92. The first step in the loop, step 94, image guidance computingplatform 30 can poll the tracker 20 via converter 26 in order to obtainthe current position of external reference marker 22 and the currentposition of non-tissue internal reference marker(s) 24. (It should beunderstood that “current” in this context is not limiting, and does notmean “instantaneous” or the like; instead, “current” is simply anadjective used to differentiate between the positions received at thisstep in the present methods from the positions received earlier, forexample.) The software can then, at step 96, construct a current vector(here, again, “current” is non-limiting) using the current positionsreceived at step 94. At step 98, the software can compare the currentvector to the dataset vectors (V1 . . . Vn) (or will compare just thecurrent positions to the tracking space coordinates) in search of thedataset vector closest to the current vector in question. Upon finding,at step 101, a match dataset vector—defined as the dataset vector (Vi)(or tracking space coordinates) most similar to the current vector (orcurrent positions, or coordinates)—the software can, at step 102, load(e.g., into memory) the image (Ii) from gated dataset 42 pointed to bythe matching look-up table dataset vector (Vi). At step 104, thesoftware can also load (e.g., into memory) the transformation (Ti)associated with the dataset vector (Vi) and the correlated image (Ii).At step 106, the system can poll tracker 20 to obtain, via converter 26,the position of instrument reference marker(s) 18. The software can, atstep 108, apply the transformation (Ti) to the position of theinstrument reference marker(s) 18 to transform that position into imagespace. At step 110, the software can superimpose (e.g., render, draw,etc.) a representation (e.g., an iconic representation) of instrument 16(or instruments, as the case may be) on the selected image (Ii) to bedisplayed on a monitor of image guidance computing platform 30.

The Navigation State 90 steps can be repeated continuously and theirperformance will provide physician 14 with a live representation of hisinstruments with respect to the instantaneous position and orientationof the anatomy in question as he image guides those instruments to theircorrect locations to deliver medical therapy.

A basic embodiment of the present methods that may be achieved using thesystem 100 software described above is a method that includes creating adataset that includes images, at least one of the images: depicting anon-tissue internal reference marker, being linked to non-tissueinternal reference marker positional information (such as a datasetvector), and being at least 2-D. In another embodiment, and as describedabove, each image in the dataset depicts a non-tissue internal referencemarker (e.g., marker(s) 24), and is linked to non-tissue internalreference marker positional information. The non-tissue internalreference marker positional information may, for example, take the formof positional coordinates or a dataset vector. The images may be 3-D CTimages or 3-D MRI images. Other embodiments of the present methodsinclude taking one or more additional steps from among those stepsdescribed above. Thus, and by way of example, another embodiment of thepresent methods includes loading a gated dataset into memory thatincludes the images, at least one of the images depicting the non-tissueinternal reference marker and being linked to a sample of a periodichuman characteristic signal. In still another embodiment, each image inthe gated dataset depicts the non-tissue internal reference marker andis linked to a sample of the periodic human characteristic signal.

Another basic embodiment of the present methods that may be achievedusing the system 100 software described above is a method that includesreceiving a position of an instrument reference marker coupled to aninstrument (e.g., a medical instrument); transforming the position intoimage space using a position of a non-tissue internal reference markerimplanted in a patient; and superimposing a representation of theinstrument on an image in which the non-tissue internal reference markerappears. In another embodiment, the transforming includes transformingthe position into image space using a transformation that is based, inpart, on the position of the non-tissue internal reference markerimplanted in the patient. And in yet another embodiment, the method alsoincludes calculating the transformation using image space coordinates ofthe internal reference marker in the image. Other embodiments of thepresent methods include taking one or more additional steps from amongthose steps described above.

Periodic human characteristic signals other than ECG signals may be usedconsistently with the steps described above. For example, respiration orhemodynamic characteristics of patient 10 could just as easily be usedas periodic human characteristic signals. If such signals are used,appropriate periodic human characteristic signal monitors should be usedas well. Furthermore, any imaging modality (not just CT or MRI) that canbe gated to a periodic human characteristic signal may be usedconsistently with the steps described above, including positron emissiontomography (PET), ultrasound, and functional MRI (fMRI).

2. Use of CINE Fluoroscopy

FIG. 6 depicts one embodiment of a system (system 200) that includescomponents (many of which are the same, and are coupled in the samefashion, as those in system 100) that can be used to perform imageguided interventions using CINE 2-D fluoroscopy as an imaging modality.Gated scanner 40 and hospital network 50 in system 100 are replaced withfluoroscope 215, which, as shown, can include fluoroscope stand 210,fluoroscope receiver unit 212 (e.g., a fluoroscope radiation receiverunit), and fluoroscope calibration jig 214. Fluoroscope 215 is coupledto image guidance computing platform 30.

One advantage of using CINE fluoroscopy as an image guidance modality isthat it can be captured during the procedure in the operating orprocedure theatre. As a result, the physician may dispense with thegating of a periodic human characteristic signal to pre-operativeimages. Generally speaking, FIG. 7 captures what will happen using CINEfluoroscopy; a non-tissue internal reference marker(s) 24 will be placedas described above and tracked as each image (I1, I2 . . . In) iscaptured using fluoroscope 215, and more specifically fluoroscopereceiver unit 212. The placement of such internal reference markers isshown in FIG. 7 with respect to the heart, and more specifically, withrespect to various stages of the heart's function (A1, A2 . . . An).Vectors (V1, V2 . . . Vn) that are based on the positions of an externalreference marker (not shown) and non-tissue internal reference marker 24(shown) are depicted in FIG. 7 in terms of the X, Y, and Z axisinformation. Those vectors will be discussed in more detail below. Afterthe image capture process is complete, the particular image mostaccurately depicting the anatomy at a particular instant can beascertained by examining the position of the non-tissue internalreference marker(s), and selecting the image that was captured when themarker was last in that particular location and orientation.

To begin the image guided intervention, patient 10 will be placed uponoperating table 12 and an ECG monitor 32 will likely be connected topatient 10 for diagnostic purposes unrelated to performing imageguidance. Fluoroscope 215 can be positioned to allow images to becaptured of patient 10 (likely in an orientation that physician 14 ismost comfortable with, such as a Right Anterior Oblique (RAO) view).Physician 14 can place an external reference marker 22 as discussedabove (e.g., in the procedural field on a location that does not movewith respect to heartbeat and respiration). One or more non-tissueinternal reference marker(s) 24 can be placed in the gross region of theanatomy intended for image guidance. Fluoroscope calibration jig 214 canbe coupled to fluoroscope receiver unit 212. All connections betweenfluoroscope 215, reference markers 22 and 24, converter 26, and imageguidance computing platform 30 can be fulfilled as depicted in FIG. 6,and information can then flow among the system 200 components.

At this time, system 200 is ready to enter the Calibration State 250 asdepicted in FIG. 8. First, physician 14 can trigger fluoroscope 215 tobegin acquiring an image signal (e.g., a CINE fluoroscopy loop). Asfluoroscope 215 begins to acquire the image signal, the live video feedcan be sent to, and received by, image guidance computing platform 30.

While fluoroscope 215 is acquiring the CINE loop, as noted with element252, the software can, as step 254 notes, sample the live video feed.Sampling consistent with step 254 can occur at a rate greater than 30 Hzso as capture enough images (e.g., image frames) such that they will,when pieced together, appear to be real time to the human eye. Ascomputing power makes faster sampling rates for more feasible, asampling rate greater than 60 Hz can be implemented in accordance withNyquist's Law.

The software can create an image (e.g., an image frame) (Ii) as denotedin FIG. 7 and, at step 256, store that image into memory. The softwarecan also poll the tracker 20 and receive, at step 258, positionalinformation for (e.g., the positions of) the reference markers (e.g.,static external reference marker 22 and non-tissue internal referencemarker(s) 24). The system can then, at step 260, construct, orcalculate, a dataset vector (see V1 . . . Vn in FIG. 7) defining theorientation of the reference markers during the instantaneousacquisition of this particular image (Ii). The software can, at step262, record the dataset vector (Vi) (or at least the positionalinformation) and the associated image (Ii) in a dataset (e.g., dataset300, which can, in at least one embodiment, take the form of a look-uptable) as depicted in FIG. 9. Step 262 may also be described as creatinga dataset that includes at least one image that depicts a non-tissueinternal reference marker, is linked to positional information about thenon-tissue internal reference marker, and is at least 2-D. FIG. 9 showsdataset 300 residing in memory 44, which can reside in image guidancecomputing platform 30. After a sufficient number of images have beencollected and stored, the software begin the transformation calculationprocess. For example, for each image (Ii), as noted by element 263, thesoftware can, at step 264, poll tracker 20 for, and can receive, theposition of the fluoroscope calibration jig 214. With this positionalinformation, the software can, at step 266, calculate a transformation(Ti) from tracking space (e.g., the tracker field coordinate space) toimage space (e.g., the fluoroscope image space) using the methodsdisclosed in U.S. Pat. No. 6,470,207. At step 268, the transformation(Ti) can be stored in association with (e.g., linked to) the image (Ii)in the look-up table associated with, or keyed by, database vector (Vi).This step may also be described as associating the transformation (Ti)with image (Ii). The software can repeat this process until a completeset of images necessary to characterize the anatomy over its entireperiodic cycle of movement have been captured and characterized.

After completion of Calibration State 250, the software moves the systeminto Navigate State 350. In this state, the software can enter aninfinite loop of events, as designated by element 352. In the first stepin the loop, step 354, image guidance computing platform 30 polls thetracker 20 via converter 26 in order to obtain the current position ofexternal reference marker 22 and the current position of non-tissueinternal reference marker(s) 24. (It should be understood that “current”in this context is not limiting, and does not mean “instantaneous” orthe like; instead, “current” is simply an adjective used todifferentiate between the positions received at this step in the presentmethods from the positions received earlier, for example.) The softwarecan then, at step 356, construct a current vector (here, again,“current” is non-limiting) using the current positions received at step354. At step 358, the software can compare the current vector to thedataset vectors (V1 . . . Vn) (or will compare just the currentpositions to the tracking space coordinates) in search of the datasetvector closest to the current vector in question. Upon finding, at step360, a match dataset vector—defined as the dataset vector (Vi) (ortracking space coordinates) most similar to the current vector (orcurrent positions, or coordinates)—the software can, at step 362, load(e.g., into memory) the image (Ii) from dataset 300 pointed to by thematching look-up table dataset vector (Vi). At step 364, the softwarecan also load (e.g., into memory) the transformation (Ti) associatedwith the dataset vector (Vi) and the correlated image (Ii). At step 366,the system can poll tracker 20 to obtain, via converter 26, the positionof instrument reference marker(s) 18. The software can, at step 368,apply the transformation (Ti) to the position of the instrumentreference marker(s) 18 to transform that position into image space. Atstep 370, the software can superimpose (e.g., render, draw, etc.) arepresentation (e.g., an iconic representation) of instrument 16 (orinstruments, as the case may be) on the selected image (Ii) to bedisplayed on a monitor of image guidance computing platform 30.

The Navigation State 350 steps can be repeated continuously and theirperformance will provide physician 14 with a live representation of hisinstruments with respect to the instantaneous position and orientationof the anatomy in question as he image guides those instruments to theircorrect locations to deliver medical therapy.

A basic embodiment of the present methods that may be achieved using thesystem 200 software described above is a method that includes creating adataset that includes images, at least one of the images: depicting anon-tissue internal reference marker, being linked to non-tissueinternal reference marker positional information (such as a vector), andbeing at least 2-D. In another embodiment, and as described above, eachimage in the dataset depicts a non-tissue internal reference marker(e.g., marker(s) 24), and is linked to non-tissue internal referencemarker positional information. The non-tissue internal reference markerpositional information may, for example, take the form of positionalcoordinates or a dataset vector. The images may be 2-D fluoroscopyimages (e.g., CINE fluoroscopy images). Other embodiments of the presentmethods include taking one or more additional steps from among thosesteps described above. Thus, and by way of example, another embodimentof the present methods includes calculating a dataset vector using aposition of an external reference marker and a position of a non-tissueinternal reference marker.

Another basic embodiment of the present methods that may be achievedusing the system 200 software described above is a method that includesreceiving a position of an instrument reference marker coupled to aninstrument (e.g., a medical instrument); transforming the position intoimage space using a position of a non-tissue internal reference markerimplanted in a patient; and superimposing a representation of theinstrument on an image in which the non-tissue internal reference markerappears. In another embodiment, the transforming includes transformingthe position into image space using a transformation that is based, inpart, on the position of the non-tissue internal reference markerimplanted in the patient. And in yet another embodiment, the method alsoincludes calculating the transformation using image space coordinates ofthe internal reference marker in the image. Other embodiments of thepresent methods include taking one or more additional steps from amongthose steps described above.

3. Non-Tissue Internal Reference Marker

An example of a non-tissue internal reference marker suitable for use asnon-tissue internal reference marker 24 for use with system 100 is shownin FIG. 11. In the case where the imaging modality used for the purposesof image guided intervention is MRI, the non-tissue internal referencemarker(s) 24 placed into the patient can be non-ferrous to meet safetyrequirements of the imaging device (e.g., gated scanner 40). FIG. 11depicts such an apparatus. Apparatus 400 includes a non-ferrous body(i.e., a body that is not made of any iron) 410 that defines a chamber412. Body 410 can be made of a material that makes it opaque to theimaging modality such that it shows up as a blank (white) spot on theimage. Such materials include platinum and titanium. A non-ferroustissue fixation member 414 is coupled (e.g., through attachment) to body410 at an end of body 410 to allow apparatus 400 to be implanted in thegross region of interest for a procedure. Member 414, as shown, can havea pig-tail shape. As a result, member 414 can be unscrewed to releasethe apparatus after completion of the procedure. Such pig-tail designsare common among temporary pacing leads in the field of cardiacelectrophysiology. The embodiment of apparatus 400 shown in FIG. 11 alsoincludes a segment 416 (such as a sheath, or a portion of a sheath)coupled to body 410. Segment 416 includes a passageway 418 that is incommunication with chamber 412. The segment can be plastic. Any portionof segment 418 that extends outside of a patient is not considered to bea part of any of the present non-tissue internal reference markers.

When apparatus 400—as a non-tissue internal reference marker—isimplanted prior to imaging, chamber 412 can remain empty. The patientinto which the apparatus is implanted can be scanned with apparatus 400implanted and segment 418 in place, which can extend outside of thepatient (e.g., outside of the patient's skin). Upon successfulcompletion of the scan, one or more ferrous tracking sensors 420 thatare configured for placement in chamber 412 and their ferrous connectingleads 422 (e.g., wires) can be introduced into chamber 412 via segment416 and locked into place. This apparatus, therefore, alleviates theneed for the tracking sensors to be non-ferrous.

As will be understood by those having skill in the art and the benefitof this disclosure, the steps disclosed above, and the techniques forcarrying them out, may be implemented in any number of various media ordevices. While described above in terms of software, it should beunderstood that the referenced software may take the form of machine(e.g., computer) readable instructions on computer readable media. Thecomputer-readable, or machine-readable media, may take many forms,including any data storage device that can store data that canafterwards be read by a computer or a computer system, including a disk,such as a floppy disk, a zip disk, or the like; a server, read-onlymemory; random access memory; CD-ROMs; a memory card; magnetic tape;optical data storage devices, SMARTMEDIA® cards; flash memory; compactflash memory; and the like. The computer readable medium can also bedistributed over network-coupled computer systems so that the computerreadable instructions are stored and executed in a distributed fashion.For example, the computer readable medium may take the form of a carrierwave such as, for example, signals on a wire (e.g., signals downloadedfrom the Internet) or those that are transmitted electromagnetically orthrough infra red means. Furthermore, when the machine readableinstructions in question have been loaded onto a given machine, thatmachine can be described as configured to take whatever actions aredefined by the instructions.

In another embodiment, any of the present methods may be embodied in anintegrated circuit, such as application specific integrated circuit(ASIC), or in a field programmable gate array (FPGA). In anotherembodiment, any of the present methods may be embodied by a combinationof hardware and software; for instance, certain instructions may beexecuted by a chip running appropriate firmware. In another embodiment,any of the present methods may be embodied by a kit, such as a softwaredeveloper's kit. Such a kit may include not only software, but also anycorresponding hardware to execute the software. For instance, a kit mayinclude a computer board along with drivers and software to be run bythat board. Those having skill in the art will recognize that thepresent methods may be implemented by other means known in the art toachieve an identical or similar result. All such means are considered tobe within the scope of the present methods and systems that includedevices configured to carry out the present methods.

The claims are not to be interpreted as including means-plus- orstep-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” or “step for,”respectively.

What is claimed is:
 1. A method comprising: creating a dataset thatincludes images, one of the images (a) depicting a non-tissue internalreference marker, (b) being linked to non-tissue internal referencemarker positional information, and (c) being at least 2-dimensional. 2.The method of claim 1, where the non-tissue internal reference markerpositional information comprises a dataset vector 3.-7. (canceled) 8.The method of claim 2, further comprising: loading a gated dataset intomemory, the gated data set including the images, one of the images (a)depicting the non-tissue internal reference marker, and (b) being linkedto a sample of a first periodic human characteristic signal.
 9. Themethod of claim 8, where each image (a) depicts the non-tissue internalreference marker, and (b) is linked to a sample of a first periodichuman characteristic signal.
 10. The method of claim 8, furthercomprising: receiving a second periodic human characteristic signal; andcomparing a sample of the second periodic human characteristic signal tothe sample of the first periodic human characteristic signal.
 11. Themethod of claim 10, where the first and second periodic humancharacteristic signals are electrocardiogram (ECG) signals.
 12. Themethod of claim 10, further comprising: recognizing a sample of thesecond periodic human characteristic signal that matches the sample ofthe first periodic human characteristic signal; and receiving (a) aposition of an external reference marker and (b) a position of thenon-tissue internal reference marker.
 13. The method of claim 12,further comprising: calculating the dataset vector using (a) theposition of the external reference marker and (b) the position of thenon-tissue internal reference marker. 14.-23. (canceled)
 24. A methodcomprising: receiving a position of an instrument reference markercoupled to an instrument; transforming the position into image spaceusing a position of a non-tissue internal reference marker implanted ina patient; and superimposing a representation of the instrument on animage in which the non-tissue internal reference marker appears.
 25. Themethod of claim 24, where the image was taken using fluoroscopy.
 26. Themethod of claim 24, where the image was taken using computed tomography(CT).
 27. The method of claim 24, where the image was taken usingmagnetic resonance imaging (MRI).
 28. The method of claim 24, where thetransforming includes transforming the position into image space using atransformation that is based, in part, on the position of the non-tissueinternal reference marker implanted in the patient.
 29. The method ofclaim 28, further comprising: calculating the transformation using imagespace coordinates of the internal reference marker in the image.
 30. Themethod of claim 29, further comprising: linking the transformation tothe image.
 31. The method of claim 30, further comprising: loading thetransformation into memory.
 32. The method of claim 24, furthercomprising: receiving an image signal that includes the image.
 33. Themethod of claim 32, further comprising: receiving a position of thenon-tissue internal reference marker in the image.
 34. The method ofclaim 33, further comprising: calculating a vector using the position35. The method of claim 34, further comprising: linking the vector withthe image.
 36. The method of claim 35, where the transforming includestransforming the position into image space using a transformation thatis based, in part, on the position of the non-tissue internal referencemarker implanted in the patient.
 37. The method of claim 36, furthercomprising: linking the transformation from tracking space to imagespace with the image.
 38. A computer readable medium comprising machinereadable instructions for carrying out the steps of claim
 24. 39. Amethod comprising: receiving an image signal that includes images, eachimage depicting a non-tissue internal reference marker; receiving aposition of the non-tissue internal reference marker in one of theimages (image I1); calculating a vector using the position; linking thevector with an image I1; linking a transformation from tracking space toimage space with image I1; receiving a current position of an instrumentreference marker coupled to an instrument; applying the transformationto the current position of the instrument reference marker; andsuperimposing a representation of the instrument on image I1.
 40. Acomputer readable medium comprising machine readable instructions forcarrying out the steps of claim 39.